Popular Mechanics

In the late night hours of October 17, and then continuing through the weekend, NASA's Lunar Laser Communication Demonstration (LLCD) on the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft made history by using a pulsed laser beam to transmit data over the 239,000 miles from the moon to Earth at a record-breaking data download speed of 622 megabits per second (Mbps). This download speed is more than six times faster than the download speed achieved by the best radio system ever flown to the moon, and the LLCD's laser space terminal is half the weight and uses 25% less power than the radio system. LLCD also demonstrated a data upload speed of 20 Mbps on a laser beam transmitted from a ground station in New Mexico to the LADEE spacecraft in lunar orbit; this speed is 5000 times faster than the upload speed of the best radio system flown to the moon. Additionally, LLCD provided continuous measurements of the distance from Earth to the fast-moving LADEE spacecraft with an unprecedented accuracy to less than half an inch (or about one centimeter).

This photograph of the optical module of the LLCD space terminal shows the 4-inch telescope and its protective window.

These first tests of the month-long communications demonstration included the successful optical transmission of two simultaneous channels carrying high-definition video streams from the ground terminal to the space terminal, where they were received and then immediately sent back optically to the Earth, thereby exercising the whole system. In addition, computer commands were sent up optically to the space terminal, while space terminal performance data were being simultaneously transmitted back to Earth. Finally, large amounts of data from the LADEE computer were relayed down in the blink of an eye; this ability to rapidly transmit enormous amounts of information will essentially revolutionize the objectives, design, and operation of future scientific space missions. All of these LLCD activities run simultaneously in the system.

The protective windows on the telescopes of the Lunar Laser Communications Ground Terminal in White Sands, N.Mex., reflect the desert sunset.

NASA's LADEE (pronounced "Laddie") satellite reached lunar orbit on October 6 after its successful launch from Wallops Island, Va., on September 6. LADEE’s primary science mission is to investigate the very thin atmosphere that exists around the moon, and the LLCD is flying along in order to demonstrate the new communications technology. The LLCD system was designed and built and is being operated by the Massachusetts Institute of Technology's Lincoln Laboratory located in Lexington, Mass. The LLCD project is managed by NASA's Goddard Space Flight Center in Greenbelt, Md. The LADEE spacecraft was built and is being operated by NASA's Ames Research Center in Mountain View, Calif.

The optical space terminal transmits a ½-watt infrared laser signal (eye safe as well as invisible to the eye) through its 4-inch (10-centimeter) telescope toward the selected ground terminal. The space terminal simultaneously receives the uplink signal transmitted from a 40-watt laser transmitted through telescopes at the ground terminal. The downlink beam is received by a novel array of highly sensitive superconducting detectors that measure the individual photons in the beam. Information is carried in both uplink and downlink laser beams using very high-speed patterns of laser pulses.

LADEE comes into view of Earth every two hours in its current orbit around the moon, and LLCD will get its turn to operate in approximately half of the possible orbits during the next four weeks, before the main LADEE science mission begins. The complete LLCD system also includes two additional ground terminals to provide more opportunities for the demonstration. The Jet Propulsion Laboratory has configured its Optical Communications Telescope Laboratory near Wrightwood, Calif., to communicate with the space terminal, and, in fact, also successfully demonstrated downlink communications a number of times during the 17 October weekend. The European Space Agency has also configured its Optical Ground Station on the island of Tenerife in the Canary Islands to communicate with the space terminal, and will be attempting links later in the month. All operations are coordinated and run from the LLCD Operations Center located at Lincoln Laboratory.

The system has been designed to operate in many optically stressing conditions such as daytime, nighttime, full moon, new moon, and high and low elevations as seen from the ground terminals. The one month of operations will allow the system to sample all these conditions in order to demonstrate the flexibility of the technology for future missions.

The demonstrated LLCD link is the longest two-way optical communications system ever achieved. The LLCD sets the stage for even higher data rates for missions to the moon as well as for greatly improved communications capabilities for missions traveling even further into space.